Process for clarifying liquids, particularly raw juice

ABSTRACT

A process for clarifying raw juice in which the proportion of solids in the retentate circuit (2, 3, 4) of an ultrafiltration or microfiltration device (1) is sharply increased during the starting time (FIG. 1). With increasing proportion of solids, the filtration yield falls off sharply and then increases again to a value which is higher than the starting value. On reaching the maximum possible filtration yield value, the proportion of solids and thereby also the filtration yield is maintained constant by regulating the amount of retentate outflow or the amount of fresh juice to be fed in. In this way the filtration yield can be significantly improved.

The invention relates to a process for clarifying liquids, particularlyraw juice from fruit, grapes, berries or other fruits and vegetables byultrafiltration or microfiltration.

BACKGROUND OF THE INVENTION

In the known processes of microfiltration and ultrafiltration, mainlytube- or plate-shaped membrane filtration modules are used. The liquidto be clarified or filtered flows crosswise to the filtration deviceover the membrane filtration surface. Thus, the clarified juice, thepermeate, is separated from the liquid containing the filtrationresidues. This procedure is repeated from time to time in one circuit ofthe retentate. During batch processing the concentration of thefiltration residues, the so-called proportion of solids, constantlyincreases.

The disadvantage of these known processes is that with increasingfiltration time and increasing proportion of solids in the retentate, adecrease occurs in the filtration yield, e.g. the amount of permeateoutflow per filtration surface unit and time unit. This decrease in thefiltration yield can amount to less than half the starting value. Forachieving a certain filtration yield, the reduced filtration yield mustbe taken into account in the design of ultrafiltration andmicrofiltration units. However, this requires large filtration surfacesand leads to expensive, partially uneconomical units with a large numberof filtration modules.

SUMMARY OF THE INVENTION

The object of the invention is to avoid the disadvantages mentioned andto develop a process, which with reduced investment costs guarantees ahigh filtration yield.

This object is achieved according to the invention in that theproportion of solids in the retentate is sharply increased byconcentrating during the starting time and after reaching the maximumfiltration yield, is maintained constant by regulation. In this way thefiltration yield, which at first decreases and then increases again whenthe proportion of solids increases further, can be maintained at a levelfar exceeding the starting value.

To ascertain the proportion of solids and to regulate the condition ofthe retentate, the proportion of solids or another quantity dependant onthe proportion of solids is measured in the retentate circuit and themeasured quantity is used to regulate the amount of retentate outflow orthe amount of fresh juice to be fed in.

In another embodiment of the invention, the amount of permeate outflowor the filtration yield is measured to regulate the condition of theretentate and the measured quantity is used to regulate the amount ofretentate outflow or the amount of fresh juice to be fed in. Themeasurement of proportion of solids can be omitted in this case, sincethe condition of the retentate is also largely dependant on thefiltration yield.

Another embodiment of the invention provides for regulating thecondition of the retentate in that both the proportion of solids oranother quantity dependant on the proportion of solids and the amount ofpermeate outflow or the filtration yield are measured, and the desiredvalue of the proportion of solids is determined by the maximumfiltration yield value which can be achieved at the beginning of theprocess. The regulation of the condition of the retentate thus takesplace depending on the proportion of solids, the desired value of whichis not however pre-set as an empirical value, but rather is ascertainedby ongoing measurement of the filtration yield.

To obtain the highest possible concentration of the proportion of solidsin the retentate in the shortest possible time during the starting time,at first a relatively small amount of retentate is used and theremaining portion of the batch amount is fed to the retentate circuitonly after achieving the desired value of the proportion of solids.

The unit for carrying out the process according to the invention ischaracterized in that, in the retentate circuit of an ultrafiltration ormicrofiltration device there is placed a measuring device to measure theproportion of solids and it is connected by a measurement line with aregulating device to regulate the condition of the retentate.

In another embodiment of the unit according to the invention, ameasuring device is placed in the permeate outflow pipe of theultrafiltration or microfiltration device to measure the amount ofpermeate outflow or the filtration yield and it is connected by ameasurement line with the regulating device to regulate the condition ofthe retentate.

In another embodiment of the unit according to the invention, themeasuring device for the filtration yield is provided in a supplementarymanner as a measuring device for the proportion of solids, and themeasuring devices are connected by measurement lines with the regulatingdevice to regulate the condition of the retentate.

According to the invention the regulation of the condition of theretentate can take place by regulating the amount of the retentateoutflow, and the regulating device is connected by a control line with aregulating valve, which is placed in a retentate outflow pipe branchedoff from the retentate circuit.

According to another feature of the invention the regulation of thecondition of the retentate can take place by regulating the amount offresh juice to be fed in, and the regulating device is connected by acontrol line with a regulating valve which is placed in a fresh juicefeed pipe.

The advantages attained with the invention consist particularly in thatby maintaining the proportion of solids in the retentate constantly at acertain value, very high filtration yield values are achieved. Thenumber of filter modules can be reduced, since the savings in filtrationsurface amounts to about 50%. The makes possible the use ofultrafiltration or microfiltration units with high yield with smallspace requirements and reduced investment costs. In this way a higheconomical efficiency of the unit results. Also the starting filtrationyield losses are significantly smaller in comparison to conventionalprocesses, since with a small amount of retentate going up to a highconcentration factor is performed in a short time. The circulatingamounts are relatively small and short pipes can be used. The pressureand energy losses are likewise slight.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail in the following drawingswhich represent several embodiments. There are shown in:

FIG. 1 a diagrammatic representation of the unit according to theinvention, with proportion of solids as the measured quantity and amountof retentate outflow as the regulated quantity,

FIG. 2 another embodiment of the unit according to the invention withproportion of solids as the measured quantity and the amount of freshjuice to be fed in as the regulated quantity and

FIG. 3 another embodiment of the unit according to the invention withthe amount of permeate outflow (filtration yield) as the measuredquantity and the amount of retentate outflow as the regulated quantity.

PREFERRED EMBODIMENTS OF THE INVENTION

The unit according to FIG. 1 consists of an ultrafiltration ormicrofiltration device 1 with a retentate circuit, which is formed by afeed pipe 2, a filter surface 3 on the retentate side and return pipe 4.On the permeate side of ultrafiltration or microfiltration device 1, thefiltered clarified juice is removed by a permeate outflow pipe 5. Theraw juice to be filtered is fed to the retentate circuit from a batchcontainer 6 by a pipe 7. In pipe 7 there is placed a feed pump 8 and infeed pipe 2 of the retentate circuit there is placed a circulating pump9. A retentate outflow pipe 10 branches off from return pipe 4 and leadsto a collecting container for the retentate which is not represented.

In feed line 2 of the retentate circuit there is placed measuring device11 by which the proportion of solids in the retentate is measured. Themeasured quantity ascertained is constantly transmitted to a regulatingdevice 13 by a measurement line 12. From regulating device 13, a controlline 14 leads to a regulating valve 15, which is placed in retentateoutflow pipe 10.

At first only a small quantity of the raw juice to be filtered isintroduced into batch container 6. The raw juice reaches the retentatecircuit by pipe 7 and is carried, by circulating pump 9 in a circuitwhich is repeated from time to time, over filter surface 3 whichseparates the clear juice from the raw juice. With increasingconcentration of the retentate, the filtration yield at first decreasesto about half of the starting value and then increases again withfurther increase in the proportion of solids to a value which is farabove the starting value. This significant improvement in the filtrationyield which has ascertained by tests is to be attributed to the factthat with higher concentration of the proportion of solids in theretentate the flow behavior is altered. It is assumed that from acertain concentration of solids the flow goes from a Newtonian behaviorto a kind of block flow. The flow boundary layer on the filter wallsharply increases in speed and decreases to a considerably smaller layerthickness. With this effect, fresh retentate reaches the filter surfaceconsiderably faster and causes an improved cleaning of the filtrationlayer by the proportion of solids in the retentate. In this way furtherdeposits are prevented which could cause a reduction in filtrationyield.

However, if the proportion of solids in the retentate increases evenmore, then only a slight further increase in filtration yield isachieved and with even further increase in the proportion of solids thecircuit is interrupted as a result of too high a proportion of solids.The empirical value of the proportion of solids which was ascertained bytests and at which the filtration yield reaches its maximum is about 5%when dried, without water soluble portions, for apple juices. This or avalue dependant on it is pre-set as the desired value in regulatingdevice 13. By measuring device 11, the condition of the retentate or theproportion of solids in the retentate is ascertained, transmitted bymeasurement line 12 and compared with the pre-set desired value inregulating device 13. As soon as there is agreement, regulating valve 15is opened by control line 14 and a regulated amount of retentate isremoved by retentate outflow pipe 10 from the retentate circuit. At thesame time as the opening of regulating valve 15 the remaining portion ofthe raw juice batch amount is fed into batch container 6, and with thehelp of feed pump 8, is fed to the retentate circuit as fresh juice. Byfurther regulating the amount of the retentate outflow, the pre-setdesired value of the proportion of solids and thereby the filtrationyield is maintained constant.

As a result of the small starting amount of raw juice at the beginningof the process it is possible to achieve the concentration of theretentate corresponding to the pre-set desired value of the proportionof solids and thereby the maximum filtration yield in the shortest timepossible. This period is between approximately 8 and 20 minutesdepending on the quantity of the different influencing factors.

Instead of the proportion of solids, another quantity dependant on theproportion of solids, such as e.g. cloudiness, viscosity, specificdensity, pressure, temperature or the flow profile of the retentate canbe measured with measuring device 11. Thus several measured quantitiescan also be used to ascertain the condition of the retentate.

Another embodiment of the invention is represented in FIG. 2. Here theamount of retentate circulated is greater in comparison to theembodiment according to FIG. 1. This makes possible a somewhat slowerregulating circuit. Regulating the condition of the retentate ormaintaining the proportion of solids constant takes place in thisembodiment not by the amount of retentate outflow, but rather by theamount of fresh juice to be fed in. From regulating device 13 a controlline 16 leads to a regulating valve 17, which is placed in a fresh juicefeed pipe 18. Fresh juice feed pipe 18, in which a circulating pump 19is placed, leads from a fresh juice container 20 to batch container 6.At the beginning of the process the proportion of solids in theretentate is driven up sharply as in the embodiment according to FIG. 1and is measured with the help of measuring device 11 in retentatecircuit 2, 3, 4. At the same time the flowthrough amount of thepermeate, which corresponds to the filtration yield, is measured withadditional measuring device 21 placed in permeate outflow pipe 5. Themeasured quantity is transmitted to regulating device 13 by measurementline 22. The regulating of the proportion of solids thus takes place notas in the embodiment according FIG. 1 by a pre-set empirical value, butrather by observation of the course of the filtration yield at thebeginning of the process. As soon as the maximum possible filtrationyield is achieved or the increase in filtration yield diminishes, theproportion of solids in the retentate achieved up to this point in timeis maintained constant. For this purpose, regulating valve 17 is openedby regulating device 13 by control line 16, so that fresh juice fromcontainer 20 can reach batch container 6 and from there retentatecircuit 2, 3, 4 by pipe 7. Maintaining constant the proportion of solidsover the entire duration of the process then takes place again bymeasuring device 11, which constantly transmits the measured proportionof solids to regulating device 13.

It is nevertheless possible to perform regulation of the proportion ofsolids in the retentate directly by the filtration yield, which dependsto a large extent on the condition of the retentate, without measuringthe proportion of solids. As FIG. 3 shows, in this case measuring device11 in retentate circuit 2, 3, 4 is omitted. In measuring device 21,which is placed in permeate outflow pipe 5, the filtration yield isconstantly measured right from the beginning and the measured quantityis fed into regulating device 13 by measurement line 22. At thebeginning of the process the unit is driven up to an increasedfiltration yield value. As soon as the maximum possible filtration yieldis achieved or the increase in filtration yield diminishes, regulatingvalve 15 is opened by control line 14 and the filtration yield or theproportion of solids in the retentate is maintained constant byregulated retentate removal over the entire duration of the process.Instead of removing the retentate, the regulation can also take place byfeeding in fresh juice as in the embodiment according to FIG. 2.

I claim:
 1. A process for clarifying liquids, particularly raw juicefrom grapes, berries or other fruits and vegetables by ultrafiltrationor microfiltration comprising the steps of subjecting a raw juice to oneof an ultrafiltration or microfiltration to obtain an initial filtrationyield of permeate of a clear juice and a retentate having solidstherein, continuing to subject the retentate to the ultrafiltration ormicrofiltration while introducing a small quantity of raw juice into theretentate to increase sharply the proportion of solids in the retentatewhere upon the filtration yield at first decreases and then increaseswith a continued increase in the proportion of solids, ascertaining themaximum filtration yield of permeate occurring during the increasing ofthe proportion of solids in the retentate, and maintaining constant theproportion of solids at which the maximum filtration yield occurs suchthat the maximum filtration yield remains constant.
 2. A process asclaimed in claim 1 and the steps of measuring the proportion of solidsin the retentate or another property of the retentate dependent on theproportion of solids therein, and regulating an amount of retentateoutflow or the amount of supplied raw juice in response to the measuredproportion or property.
 3. A process as claimed in claim 1 and the stepsof measuring an amount of permeate outflow or filtration yield, andregulating an amount of retentate outflow or the amount of supplied rawjuice in response to the measured permeate outflow or filtration yield.4. A process as claimed in claim 1 and the steps of measuring theproportion of solids in the retentate or another property of theretentate dependent on the proportion of solids therein, measuring anamount of permeate outflow or filtration yield, and determining theproportion of solids occurring at a maximum filtration yield achieved atthe beginning of the process.
 5. A process as claimed in claim 1 and thesteps of utilizing only a relatively small amount of retentate duringthe starting of the process, and feeding a remaining portion of a batchof raw juice into the retentate circuit only after a predeterminedproportion of solids in the retentate is attained.